U.S. patent number 5,774,637 [Application Number 08/150,815] was granted by the patent office on 1998-06-30 for cordless printer control device.
This patent grant is currently assigned to ITI Innovative Technology Ltd.. Invention is credited to Alan P. Haber, Simon M. Kahn.
United States Patent |
5,774,637 |
Haber , et al. |
June 30, 1998 |
Cordless printer control device
Abstract
A printer control device which operates via a cordless link to
control a dedicated printer in a shared access mode, allowing
access by an alternate computer. In the preferred embodiment, the
cordless printer control device operates in an environment in which
a host computer is directly connected to a dedicated printer which
operates in a normal printing mode. The device is provided as a
pair of compact add-on units, a transmitter unit connected to a
portable computer and a receiver/switch unit connected to the
dedicated printer. The pair of units operate to provide an infrared
transmission link by which an alternate/portable computer can
detect a break in the normal printing mode and temporarily access
the dedicated printer for printing tasks. The receiver/switch unit
is provided with a time-out switch which operates to allow the
alternate computer to gain access to the printer only if during a
predetermined interval, the dedicated printer is not busy with a
printing task already assigned to it. Once the portable computer
has gained temporary access, the time-out switch protects its
continued use of the dedicated printer without allowing the host
computer to regain control until the task is completed.
Inventors: |
Haber; Alan P. (Ramot,
IL), Kahn; Simon M. (Jerusalem, IL) |
Assignee: |
ITI Innovative Technology Ltd.
(Jerusalem) N/A)
|
Family
ID: |
22536101 |
Appl.
No.: |
08/150,815 |
Filed: |
November 12, 1993 |
Current U.S.
Class: |
358/1.15;
358/1.13 |
Current CPC
Class: |
G06K
15/00 (20130101); G06F 3/1292 (20130101); G06F
3/1236 (20130101); G06F 3/1204 (20130101); G06K
2215/0005 (20130101) |
Current International
Class: |
G06K
15/00 (20060101); G06F 3/12 (20060101); G06K
015/00 () |
Field of
Search: |
;395/112,114,106,101,113,828,800,837-838,865-868,286,311,601
;370/94.1,913,349,389,334,342 ;364/424.04
;358/442,468,401,407,408,434-439 ;359/154,118,143,165
;455/31.1,69,115,151.2,95 ;399/1-2,8 ;347/142 ;235/432,379,380
;340/825.72,825.69 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Coles, Sr.; Edward L.
Assistant Examiner: Popovici; Dov
Attorney, Agent or Firm: Langer; Edward
Claims
We claim:
1. A cordless printer control device for controlling a printer
dedicated by a hard-wired link to a host computer, to enable
shared, cordless printing on the dedicated printer in accordance
with printing tasks directed by an alternate computer not linked to
the dedicated printer by a hard-wire, said device comprising:
means for generating a set of printer data and control information
signals in accordance with data available at a printer output port
of the alternate computer;
means for transmitting said printer data and said control
information signals via a cordless link;
means for receiving said transmitted printer data and said control
information signals over said cordless link; and
switching means being connected to the hard-wired link between the
dedicated printer and the host computer, and being connected by a
T-connection to said cordless link via said receiving means,
said switching means being operable in one of normal and temporary
shared access modes to control the dedicated printer respectively,
via the host computer through the hard-wired link in said normal
mode, and via the alternate computer through said T-connected
cordless link in said temporary shared access mode, in accordance
with said printer data and said control information signals,
without requiring cabling changes in the hard-wired link,
wherein said switching means comprises a timer defining a
predetermined interval beyond which inactivity of the host computer
enables the alternate computer to control the dedicated printer in
said temporary shared access mode,
and said timer defines a predetermined period beyond which
inactivity of the alternate computer enables the host computer to
regain control of the dedicated printer from said temporary shared
access mode, said predetermined period exceeding a time period
associated with an unintended interruption in transmission of said
printer data.
2. The device of claim 1 wherein said cordless link is a
bi-directional infrared communication link.
3. The device of claim 1 wherein said cordless link is a low power
RF communication link.
4. The device of claim 1 wherein said means for generating and
means for transmitting said printer data and said control
information signals is connected to said printer output port of the
alternate computer via a standard connector used for connection to
a printer.
5. The device of claim 4 wherein said standard connector is adapted
for connection to a parallel printer port.
6. The device of claim 1 wherein said switching means is connected
to said dedicated printer via a standard input printer port of said
dedicated printer, and is connected to said host computer via a
standard connector of said host computer used for connection to a
printer.
7. The device of claim 1 wherein said means for generating said
printer data and said control information signals includes means
for generating an error correction format for transmission of said
printer data.
8. The device of claim 1 wherein said means for generating said
printer data and said control information signals comprises a
serial data communication protocol allowing for transmission of
data words, error correction words and control signal words in
concert with appropriate acknowledge words to verify reception.
9. The device of claim 1 for controlling selected ones of a
plurality of dedicated printers, wherein said means for generating
said printer data and said control information signals provides an
identification code for controlling in accordance therewith a
selected one of said plurality of dedicated printers.
10. A method of controlling a printer dedicated by hard-wired link
to a host computer, to enable shared, cordless printing on the
dedicated printer in accordance with printing tasks directed by an
alternate computer not linked to the dedicated printer by a
hard-wire, said method comprising the steps of:
generating a set of printer data and control information signals in
accordance with data available at a printer output port of the
alternate computer;
transmitting said printer data and said control information signals
via a T-connected cordless link;
receiving said transmitted printer data and said control
information signals over said T-connected cordless link; and
switching between one of normal and temporary shared access modes
to control the dedicated printer respectively, via the host
computer through the hard-wired link in said normal mode, and via
the alternate computer through said T-connected cordless link in
said temporary shared access mode, in accordance with said printer
data and said control information signals, without requiring
cabling changes in the hard-wired link,
wherein as part of said switching step, a predetermined interval is
defined beyond which inactivity of the host computer enables the
alternate computer to control the dedicated printer in said
temporary shared access mode, and
a predetermined period is defined beyond which inactivity of the
alternate computer enables the host computer to regain control of
the dedicated printer from said temporary shared access mode, said
predetermined period exceeding a time period associated with an
unintended interruption in transmission of said printer data.
11. The method of claim 10 wherein said transmitting step is
performed via a bi-directional infrared communication link.
12. The method of claim 10 wherein said transmitting step is
performed via a low power RF communication link.
13. The method of claim 10 wherein said generating step comprises
providing a serial data communication protocol allowing for
transmission of data words, error correction words and control
signal words in concert with appropriate acknowledge words to
verify reception.
14. The method of claim 10 for controlling selected ones of a
plurality of dedicated printers, wherein said generating step
provides an identification code for controlling in accordance
therewith a selected one of said plurality of dedicated printers.
Description
FIELD OF THE INVENTION
The present invention relates to computer peripheral devices, such
as printers and associated data control devices, and more
particularly, to a printer control device for cordless control of a
dedicated printer in a shared print mode.
BACKGROUND OF THE INVENTION
The continuing proliferation of portable computing and
wordprocessing equipment has made the portable office a reality.
Especially apparent today in all transportation terminals are an
increasing number of traveling business executives, waiting for a
departure while busily updating their laptop computers with meeting
notes, for example. When the executive arrives at his destination
or returns to the office, there exists an immediate need to print
these notes, and this determines how quickly the executive can reap
the fruits of the work/travel time. Temporary access by a portable
computer to a dedicated printer which is already connected to
office computers is problematic, since this requires manipulation
of the connections for each printer station, and cabling and plug
adapters. This involves disturbing the existing hardware
connections, changing printing modes, and causing unecessary
downtime, and possibly even equipment damage.
Therefore, it would be desirable to provide a device to enable a
portable computer to temporarily access a dedicated printer without
requiring cabling and connection changes.
SUMMARY OF THE INVENTION
Accordingly, it is a principal object of the present invention to
overcome the above-mentioned problems associated with printing
arrangements involving temporary access to dedicated printers, and
provide a printer control device which operates via a cordless link
to control a dedicated printer in a shared access mode, allowing
access by an alternate computer.
In accordance with a preferred embodiment of the present invention,
there is provided a cordless printer control device for controlling
a printer dedicated to a host computer, said device comprising:
means for generating a set of printer data and control information
signals in accordance with data available at a printer output port
of an alternate computer;
means for transmitting said printer data and control signal set via
a cordless link;
means for receiving said transmitted printer data and control
signal set; and
switching means connected to said receiving means, the dedicated
printer, and the host computer,
said switching means being operable in one of normal and temporary
access modes to control the dedicated printer via respectively, the
host computer in said normal mode, and said alternate computer in
said temporary access mode, in accordance with said printer data
and control signal set.
In the preferred embodiment, the inventive cordless printer control
device operates in an environment in which a host computer is
directly connected to a dedicated printer which operates in a
normal printing mode. The cordless printer control device is
provided as a pair of compact add-on units, a transmitter unit
connected to a portable computer and a receiver/switch unit
connected to the dedicated printer. The pair of units operate to
provide an infrared transmission link by which an
alternate/portable computer can detect a break in the normal
printing mode and temporarily access the dedicated printer for
printing tasks.
In order for the portable computer to gain access to the dedicated
printer, the receiver/switch unit is provided with a time-out
switch which operates to allow access only if during a
predetermined interval, the dedicated printer is not busy with a
printing task already assigned to it.
Once the portable computer has gained temporary access, the
time-out switch protects its continued use of the dedicated printer
without allowing the host computer to regain control until the task
is completed. When the time-out switch determines that the printer
is not busy during a predetermined interval, this indicates its
re-availability to the host computer.
A feature of the invention is its ability to maintain the temporary
access mode even during short interruptions of the line-of-sight
infrared link between the transmitter and receiver.
Another feature of the invention is the use of standard connectors
between computer/printer ports and the control device.
Still another feature of the invention is the use of a serial data
communication protocol allowing for combined transmission of data,
error correction and control signals.
Other features and advantages of the invention will become apparent
from the following drawings and description.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention with regard to the
embodiments thereof, reference is made to the accompanying
drawings, in which like numerals designate corresponding elements
or sections thoughout, and in which:
FIG. 1 is an overall schematic diagram of a cordless printer
control device constructed and operated in accordance with the
principles of the present invention;
FIG. 2 is schematic block diagram of a transmitter portion of the
device of FIG. 1, for transmission of print control signals and
data from a portable computer to a receiver portion of the
device;
FIG. 3 is a schematic block diagram of the receiver portion of the
device of FIG. 1, for controlling a dedicated printer;
FIG. 4 is a schematic block diagram of a switch portion of the
device of FIG. 1, for determining a printing mode;
FIGS. 5A-B show a circuit schematic diagram of the transmitter
portion of FIG. 2;
FIGS. 6A-B show a circuit schematic diagram of the receiver portion
of FIG. 3;
FIGS. 7A-F show a circuit schematic diagram of the switch portion
of FIG. 4;
FIG. 8 is a circuit schematic diagram of an infrared (IR)
transmitter used in the transmitter and receiver portions of the
device;
FIG. 9 is a circuit schematic diagram of an infrared (IR) receiver
used in the transmitter and receiver portions of the device;
and
FIGS. 10-11 are flowchart diagrams of the operational sequence of
the cordless printer control device of FIG. 1.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Referring now to FIG. 1, there is shown an overall schematic block
diagram of a cordless printer control device 10 constructed and
operated in accordance with the principles of the present
invention. Device 10 comprises a transmitter portion 12, a receiver
portion 14, and a switch 15, operating in a computer system
comprising a portable computer 16, a host computer 18, and a
dedicated printer 20. In the following description, portable
computer 16 represents any computer, portable or otherwise, and
this terminology is used to distinguish it from host computer 18,
which is typically cable-connected to dedicated printer 20.
As will be described further herein, device 10 operates to provide
a cordless, bi-directional infrared link between portable computer
16 and printer 20, such that printer 20 will accept control signals
and data for printing which is transmitted via the infrared link.
Thus, device 10 can interrupt the normal printing mode in which
printer 20 operates to print data from host computer 18, and cause
it to switch its operational mode to allow for temporary access by
portable computer 16. The exchange of data and control signals
between portable computer 16 and printer 20 is transparent to both,
so that the normal printing mode is interrupted by device 10 in an
orderly fashion, and after the printing task is completed, control
is then restored to host computer 18.
Referring now to FIG. 2, there is shown a schematic block diagram
of a transmitter portion 12 of the device of FIG. 1, for
transmission of printer control signals (via control words) and
data from portable computer 16 to dedicated printer 20. Transmitter
portion 12 comprises a data buffer 22 connected to the parallel
printer port available in portable computer 16. Data buffer 22
transfers the data in 8-bit format for conversion in a parallel to
serial converter 24, and the data is then processed by an error
correction coding circuitry 26, which places the data in an error
correction format. The formatted data is transferred to an infrared
transmitter 28, comprising the transmission end of a cordless IR
link for serial data transmission to dedicated printer 20.
As described further herein, infrared transmitter 28 produces IR
pulses for transmission of data in serial fashion to receiver
portion 14, where it is fed through switch 15 once temporary access
to printer 20 is gained, such that the normal printing mode via
host computer 20 is suspended.
Transmitter portion 12 also comprises a control word generator 30
for generating control words for transmission via the cordless link
to printer 20. A computer control signal latch 32 transfers several
control signals, including a Prime signal, which is to initialize
printer 20, a Select signal instructing the printer that a control
signal is being transferred, or an Auto signal instructing it to
automatically add a line feed at every carriage return. Control
word generator 30 also receives control signals from printer 20 via
IR receiver 34, and these are decoded by decoder 36. Certain
control signals are transferred to portable computer 16 via printer
control signal latch 38. These signals include PE (paper empty)
signal, or a Fault signal, indicating a problem with printer
20.
Decoder 36 also provides a control signal to the acknowledge pulse
generator 40, which in turn provides an acknowledge pulse (Ack) to
portable computer 16, completing the handshake protocol between
portable computer 16 and printer 20.
The portable computer begins the sequence of operation by providing
8 bits of data output on its parallel port (D0-D7), which is
available to data buffer 22. A data strobe signal (DS) is then
provided, which latches the data into data buffer 22, and indicates
that printer 20 is to use the data in a printing task. A busy
signal is generated by data buffer 22 and transferred to computer
16, indicating the data is now being transferred, and no more data
is sent by computer 16 until this signal is released and
acknowledge pulse is received.
After the data has been converted into serial format in converter
24 and provided with an error correction format in circuitry 26,
the data is transmitted over the IR link, and when receiver portion
14 has received the data and is ready to accept more data, it sends
an acknowledge word over the IR link to transmitter portion 12.
Upon receipt of the acknowledge word, transmitter portion 12
releases the busy signal and sends an acknowledge pulse to computer
16, indicating it is ready to accept more data. Decoder 36 will
determine if the pulse received from printer 20 indicates that the
data has been received, and then the acknowledge pulse generator
transfers the acknowledge pulse to computer 16, and releases the
busy signal.
If receiver portion 14 has not received data, or the data has been
distorted, decoder 36 generates a signal which is fed to control
word generator 30, advising it of the current status. Control word
generator 30 operates to correct the error, by resending the data,
with a new control word indicating a resend.
Referring now to FIG. 3, there is shown a schematic block diagram
of a receiver portion 14 of the device of FIG. 1, for controlling
dedicated printer 20. Receiver portion 14 comprises an infrared
receiver 42 to receive the infrared pulses containing data and
control words from transmitter portion 12, after which the data is
transferred for conversion to parallel form by serial to parallel
converter 44, and then stored in data buffer 46. The data is then
fed to error detection circuitry 48, and if errors are detected, an
error word generator 50 operates to provide an IR transmitter 52
with an error word which will be transferred to the transmitter
portion 12 and decoded in decoder 36, as described previously.
A control word detection circuit 54 determines if a control word or
data for printing has been received. The information protocol
contains a 9th bit for differentiating between data and control,
and if a control word is transferred, a printer control signal
latch 56 changes the status of printer 20, using the Auto, Prime or
Select signals, described above. Using this method, control words,
error correction words and data are sent in concert over the serial
IR link.
If data for printing has been received, control signal generator 58
sends a data strobe signal and printer 20 answers with a busy
signal, indicating printer 20 is busy printing the data. When
printer 20 has finished printing the data, the busy signal is
released and an acknowledge pulse is fed by printer 20, and
transferred to acknowledge word generator 60, for transfer via IR
transmitter 52 back to transmitter portion 12. Once the data strobe
signal is given, the data can be transferred directly to printer
20. If there is a change in the status of printer 20, control
signals such as PE, Select or Fault are provided to computer
control signal latch 62, and via control word generator 64, for
transfer via IR transmitter 52 to transmitter portion 12, to notify
computer 16.
As described earlier, in the normal mode of printer 20 operation,
data from host computer 18 is printed by printer 20. In accordance
with the principles of the present invention, the operational mode
of printer 20 can be altered to allow for temporary access by
portable computer 16 for printing tasks. This is achieved by
operation of switch 15 which enables printer 20 to be shared by
host computer 18 and portable computer 16.
Referring now to FIG. 4, there is shown a schematic block diagram
of a switch portion 15 of the device 10 of FIG. 1, for determining
a printing mode. Switch 15 comprises a tri-state buffer 66a,b which
transfers all the control signals and data exchanged between
printer 20 and each of portable computer 16 and host computer
18.
Tri-state buffer 66a,b is a standard type of buffer used to allow
two different signals to share the same wire. Thus, a parallel
signal path exists through tri-state buffer 66a,b for each of the
data signals D0-D7 and the data strobe signal, as well as the
printer control signals. A timeout switch 68 is provided in the
signal path for the data strobe signal, and switch 15 determines
whether portable computer 16 or host computer 18 has gained control
of printer 20.
If host computer 18 is active in the normal printing mode, its data
strobe signal will pulse continually. If no pause is detected in
this signal for over 5 seconds, timeout switch 68 will not allow
portable computer 16 access, by blocking its data strobe signal
path from receiver portion 14 through tri-state buffer 66a. If
however, host computer 18 is silent and not active, receiver
portion 14 of device 10 can gain temporary access to printer 20,
when tri-state buffer 66b blocks the data strobe signal path of
host computer 18. Time out switch 68 can be adjusted for a range of
time periods, to vary the "silent" period enabling access to
printer 20 by the other computer.
The operation of timeout switch 68 is useful to avoid unintended
"grabbing" of access to printer 20 by one of the computers. For
example, if portable computer 16 is sending data and the IR link is
blocked by an individual passing between transmitter portion 12 and
receiver portion 14, the short duration of the computer "silent"
period is not interpreted as allowing access by the host computer
18.
If the IR link is blocked, the data transmission is completely
interrupted, and once restored, the error detection circuitry will
be needed to insure that printer 20 does not print mistakes at the
beginning and end of the interruption. An error correction
detection protocol is used in which the data has a control word
associated with it. If the data is not received properly, an error
word will be sent indicating this, and the data will be resent. If
no acknowledge pulse is sent, the assumption is that the data is
lost, and it is resent after a programmable delay.
In FIGS. 5A-B, there is shown a circuit schematic diagram of
transmitter portion 12 of FIG. 2, which can be implemented in an
Intel 87C51 or equivalent microcontroller 70 in accordance with
skill of the art electronic design techniques. The data is provided
by signals D0 through D7 via a cable connector 71 from computer 16,
which is the input to microcontroller 70 ports P1.0-P1.7. The data
strobe signal is provided to port P3.2 as an interrupt, indicating
to microcontroller 70 that data is available for transfer.
Simultaneously, the data strobe signal is fed to the input of J-K
flip-flop 72 (type HC-109), which answers the data strobe signal by
providing an output busy signal within 1 microsecond. Flip-flop 72
is employed separately for this, since it responds faster than
microcontroller 70, to indicate to portable computer 16 that the
data strobe signal has been received and data transfer is
underway.
Microcontroller 70 responds to the data strobe signal by reading
the data and converting it to serial format, and generates the
control word and the serial data word. These are sent out serially
via the UART of microcontroller 70 which is listed as the serial
data output line 74. Microcontroller 70 then waits for an
acknowledge word to be returned on the serial input line 76, from
the acknowledge word generator 60 in receiver 14 (FIG. 3).
By operating microcontroller 70 at 12 MHz, a transmission baud rate
of 375K can be achieved. Greater speeds are available by increasing
the clock rate of microcontroller 70.
Also provided by microcontroller 70 are the Error, Select, PE, and
acknowledge pulse signals, which are sent to portable computer 16
as control signals. The status of these signals is provided by a
control word sent from receiver portion 14. The acknowledge pulse
generated in microcontroller 70 is accompanied by busy set and
reset signals, respectively, from ports P0.0 and port P0.1. The
busy reset removes the busy signal on the next clock pulse on
flip-flop 72. The acknowledge pulse from port P0.2 is sent to
computer 16 to complete the handshake protocol. Port P0.6 drives an
LED indicating that the device 10 is operating. Ports P2.0 and P2.1
are used for input of Auto and Select printer control signals.
Microcontroller 70 port P3.3 is the input for an interrupt signal
used to initialize printer 20, and reset it. In response to this
signal, microcontroller 70 generates a control word in control word
generator 30, to provide an initialization routine, and send it out
on the IR link, while waiting for the acknowledge word to be
returned.
In FIGS. 6A-B, there is shown a circuit schematic diagram of
receiver portion 14 of FIG. 3, also implemented in an 87C51
microcontroller 80. Once the data is received via the IR receiver
42 (FIG. 3) and inputted to microcontroller 80 on port P3.0, a
serial to parallel conversion of the data is performed in
microcontroller 80. The data is then sent for error detection
decoding, and if an error is found, error word generator 50
operates to send a signal via the UART on port P3.1. If a control
word was received containing control signal information, these
control signals are provided on the printer control signal latch
56, such as ports P1.0, P1.1, and P1.2, and are sent via
non-inverting buffers to switch 15.
Otherwise, if printing data was received, then it is provided on
ports P0.0-P0.7, and the data strobe signal is provided on port
P1.0. A busy signal is then generated by printer 20 and is fed to
microcontroller 80 on port P2.0. When printer 20 completes printing
the data, the busy signal is released and an acknowledge pulse is
sent, which is received as an interrupt on port P3.2. When this
interrupt is received, the acknowledge word generator 60 transfers
the acknowledge word via the IR link back to the transmitter
portion 12.
FIGS. 7A-F show a circuit schematic diagram of the switch portion
15 of FIG. 4. Data from portable computer 16 is transferred via the
transmitter portion 12 and IR link, and is then transmitted to
receiver portion 14, which is connected to switch portion 15 a
T-connected via cable connector J2 (portion 51). Host computer 18
is connected to switch 15 via cable connector J3, and switch 15 is
connected to printer 20 via cable connector J1. When a data strobe
signal is fed through connector J2 from portable computer 16 to a
one-shot device IC7A a timeout function is generated which
indicates that host computer 18 may not access printer 20, since
portable computer 16 has gained temporary access. The one-shot
device IC7A is programmable to generate a 5 second disable signal
which prevents transfer of data via connector J3, so that only
control signals passing via IC1, IC2 and IC3 are transferred
between portable computer 16 and printer 20.
While portable computer 16 has gained temporary access to printer
20, and a data strobe signal continues to appear, for at least 5
more seconds host computer 18 will see a busy signal 82 and a
de-selected mode signal 84, which are transferred via IC3,
indicating to host computer 18 that printer 20 is off-line.
If the timeout period is exceeded, the normal printing mode may be
restored such that host computer 18 communicates with printer 20,
and control signals will be passed between them via connector J3
and IC4, IC5 and IC6. In this mode, portable computer 16 will see a
busy signal 86 and a de-selected mode signal 88, indicating to
portable computer 16 that printer 20 is off-line.
FIG. 8 is a circuit schematic diagram of infrared (IR) transmitters
28, 52 used in the transmitter 12 and receiver 14 portions of
device 10. IR transmitters 28, 52 each comprise a one-shot device
having two sections V1A and V1B, wired in reverse such that each is
sensitive to an opposite pulse edge polarity. Th outputs of V1A and
V1B are connected in wired OR fashion, and fed to a pair of
transistors Q1 and Q2 wired in a Darlington arrangement.
Transistors Q1 and Q2 drive three infrared LED diodes, D1-D3.
In operation, serial data 74 being sent from microcontroller 70,
for example, is fed into one shot-device V1A and V1B, and on a
negative going edge one-shot V1A is fired, and on a positive going
edge one-shot V1B is fired. The output of V1A and V1B triggers
transistors Q1, Q2, and LEDs D1-D3 will then generate the burst of
infrared light. In this fashion, both a positive going transition
or a negative going transition of the serial data generates an
outgoing pulse from IR transmitter 28.
FIG. 9 is a circuit schematic diagram of infrared (IR) receivers
34, 42 used in transmitter 12 and receiver 14 portions of device
10. IR receivers 34, 42 each comprise three infrared detectors 90
wired in parallel, which feed an operational amplifier U3. The
output of U3 drives a transistor Q3 and inverter U4 pair, with a 5K
ohm potentiometer R1 allowing adjustment of the threshold level to
reject noise. Inverter U4 feeds its output to a flip-flop 92, which
is a simple latch set in a toggle mode.
In operation, IR detectors 90 receive the infrared pulse and
transfer the information received to amplifier U3, which drives
transistor Q3, and the output of inverter U4 operates flip-flop 92.
Flip-flop 92 responds to every pulse as either a positive going or
negative going edge, so every time it receives a pulse, it clocks
the latch to change the status from either high (1) to low (0), or
from a low back to a high state. In this fashion, the original
transition of high to low is reassembled at the receiver portion
14.
The latch provided by flip-flop 92 is initialized in accordance
with the data protocol which considers a high state as no data, and
a start bit as a low state. Transmitter portion 12 and receiver
portion 14 and their respective microcontrollers 70, 80 follow the
same protocol, such that during initialization with no data, both
latches start in a high state.
Thus, with both latches in a high state, the first pulse received
causes flip-flop 92 to drop to a low state, which is the start bit.
The reset signal 94 is provided by microcontrollers 70, 80 to reset
flip-flop 92 either if an error condition is detected or whenever
IR transmitters 28, 52 are active so that no data transmitted is
received and returned. Thus, using the reset function, IR
transmitters 28, 52 can be shut-off immediately during
transmission.
It will be appreciated by those skilled in the art that the IR link
may be replaced by a communication link using low power RF, with
appropriate modifications. In addition, where there are several
dedicated printers 20 within range of the IR link, each may be
distinctly identified in the data communication protocol by use of
an identification code in the control words, so that only the
desired printer 20 responds.
FIGS. 10-11 are flowchart diagrams of the operational sequence of
the cordless printer control device 10 of FIG. 1. The flow charts
of FIGS. 10-11 can be converted to assembler language for use in
microcontrollers 70, 80, in accordance with skill of the art
software programming techniques.
In FIG. 10, the operational sequence of transmitter portion 12 is
shown, which begins in block 95 where microcontroller 70 is
initialized so that it can handle the appropriate signals. In block
96, a wait state is entered while waiting for a data strobe from
portable computer 16 advising that there is data to be sent to
printer 20. Upon receipt of the data strobe signal in block 98, in
block 100 a control word is prepared to accompany the data for
error detection.
In block 102, the data and the control word are transmitted
together to receiver portion 14 where an error check is made. The
operational sequence then waits in block 104 for an acknowledge
pulse from printer 20, and upon receipt of an acknowledge, an
acknowledge word is sent to transmitter portion 12, which then
transfers an acknowledge pulse to portable computer 16. If an
acknowledge word is not received, the operation returns to block
100 where the control word for error detection is generated again,
and the data is resent, until a good acknowledge word is received
from receiver portion 14 and printer 20. Upon receipt of a good
acknowledge word, in block 106 this is sent to computer 16 and the
operation returns to the wait state in block 96.
In FIG. 11, the operational sequence of receiver portion 14 is
shown, beginning in block 108 with initialization of
microcontroller 80. The operation proceeds to block 110 where a
wait state is entered, awaiting receipt of serial data which is
either a control word or the data from transmitter portion 12. Upon
receipt of data in block 112, it is checked for errors in block
114. If errors are detected in block 116, in block 118 an error
word will be sent back to transmitter portion 12 and operation will
return to the wait state in block 110.
If there are no errors in the serial data received, this means it
is data to be sent to printer 20. In block 120 the data is sent to
printer 20 and in block 122, a wait state is entered, awaiting
receipt of an acknowledge pulse from printer 20. Upon receipt of a
printer acknowledge pulse in block 122, a serial acknowledge word
is sent to transmitter portion 12 in block 124, and operation
returns to the wait state in block 110.
Having described the invention with regard to certain specific
embodiments thereof, it is to be understood that the description is
not meant as a limitation, since further modifications may now
suggest themselves to those skilled in the art, and it is intended
to cover such modifications as fall within the scope of the
appended claims.
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